TRAF2 mediates JNK and STAT3 activation in response to IL-1β and IFNγ and facilitates apoptotic death of insulin-producing β-cells

Abstract

Interleukin-1β (IL-1β) and interferon-γ (IFNγ) contribute to type 1 diabetes (T1D) by inducing β-cell death. Tumor necrosis factor (TNF) receptor-associated factor (TRAF) proteins are adaptors that transduce signaling from a variety of membrane receptors including cytokine receptors. We show here that IL-1β and IFNγ upregulate the expression of TRAF2 in insulin-producing INS-1E cells and isolated rat pancreatic islets. siRNA-mediated knockdown (KD) of TRAF2 in INS-1E cells reduced IL-1β-induced phosphorylation of JNK1/2, but not of p38 or ERK1/2 mitogen-activated protein kinases. TRAF2 KD did not modulate NFκB activation by cytokines, but reduced cytokine-induced inducible nitric oxide synthase (iNOS) promotor activity and expression. We further observed that IFNγ-stimulated phosphorylation of STAT3 required TRAF2. KD of TRAF2 or STAT3 reduced cytokine-induced caspase 3/7 activation, but, intriguingly, potentiated cytokine-mediated loss of plasma membrane integrity and augmented the number of propidium iodide-positive cells. Finally, we found that TRAF2 KD increased cytokine-induced production of reactive oxygen species (ROS). In summary, our data suggest that TRAF2 is an important mediator of IL-1β and IFNγ signaling in pancreatic β-cells.